The invention is directed to an arrangement for generating high voltage from a low-voltage supply source, preferably a commercially available battery or an accumulator using a charge reservoir which can be charged and recharged, via a charge pump, to at least a desired high voltage, wherein a first switching device regulates a supply of electric charge from the charge reservoir to a storage capacitor.
The invention is further directed to a method for generating high voltage from a low-voltage supply source, particularly from a commercially available battery that is used as a power supply source for a large number of electrical and electronic devices.
There are many small, portable electric or electronic devices that are supplied with power from a battery, wherein a low voltage that is a high voltage in comparison to the battery or accumulator voltage is needed within the device. Such a device contains, for instance, an optoelectronic measurement system for distances of up to 100 m with an accuracy of a few millimeters. Optoelectronic measuring systems of this type have become important in the construction industry and in plant engineering, among other areas, particularly because such systems eliminate the need to use defined target markings on the object whose distance is to be determined from an observation point or reference point. As a result, setup time and manufacturing time in the construction field, among others, can be reduced and costs can be lowered as well as manufacturing tolerances reduced. Optoelectronic measurement systems of this type are described, for example, in EP 0 701 702 B1, DE 196 43 287 A1 and U.S. Pat. No. 4,403,857. Reference is also made to a new proposed optoelectronic distance measurement system, which is the subject matter of German Patent Application 100 06 493.0.
An important performance feature of these types of optoelectronic measurement devices is their dynamics, which should be as extensive as possible in order to process very weak measurement signals as well as relatively strong measurement signals. Avalanche photodiodes, which are recommended as a rule, are used as receiver elements to guarantee the required dynamic behavior, i.e., to ensure detection of very weak measurement signals. However, since avalanche photodiodes (APDs) must be operated at comparatively high off-state or blocking voltages of, e.g., 70 V to 250 V, an arrangement is required for generating high voltage with as little interference as possible. Since the APDs which are used as receiver elements are operated in the blocking direction below their breakdown voltage and, on the other hand, since only very low light outputs are detected, it is only necessary to take into account very small photocurrents. These photocurrents, including dark currents, are in the range of about 1 nA to 100 nA. Therefore, the high-voltage source, which is supposed to supply the blocking voltage, is only required to deliver a very low electrical output.
In general, initially, an alternating voltage is generated to generate the high voltage from the battery voltage of, for example, 3 V. According to one possibility, the alternating voltage is fed to a transformer on the primary side and subsequently transformed to high voltages. The secondary-side high alternating voltage is then rectified by diodes and filtered via capacitors and possibly stabilized by a regulator. This regulation of high voltage is usually carried out by changing the pulse width ratio of the primary-side alternating voltage, which corresponds to a pulse width modulation signal.
Another possibility for generating high voltage comprises the use of switched currents in coils. Generally, a transistor which is driven by a pulse width modulation signal is used as switch. Directly after the coil current is switched off, initially, the current continues to flow because of the continuity compelled by the inductance and, with every switch-off process, charges a capacitor via a diode. The diode prevents the charged capacitor from discharging due to charge return. In this arrangement, stabilization, i.e., the regulation of the high voltage, is carried out by the pulse width ratio of the alternating voltage driving the transistor. An arrangement of this type is also known as a charge pump because electrical charges are pumped into the capacitor when the coil current is turned off.
As was already stated, one problem for high-accuracy distance measurement on technical surfaces, e.g., a concrete wall, by use of an optoelectronic distance measurement system is the problems in detecting very weak reflection signals. Accordingly, the measurement system tolerates only very low electronic noise interference. However, the switching processes mentioned above, in connection with the generation of high voltage, lead to interference when currents are switched over in the coil or coils; increasing the noise as a whole and thus reducing the sensitivity of the distance measurement.
It is, thus, the object of the invention to provide a method and an arrangement for generating high voltage from a low-voltage supply source, in which there is no interference and no additional noise during the useful application of such high voltage.
In accordance with the invention there is provided an arrangement for generating high voltage from a low-voltage supply source, especially a commercially available battery or accumulator using a charge reservoir which can be charged and recharged via a charge pump, wherein a first switching device regulates the supply of electrical charge from the charge reservoir to a storage capacitor at which the desired high voltage can be tapped and a second switching device regulates the discharge from the storage capacitor when the storage capacitor is overcharged.
According the invention, the high voltage can be rendered extensively free from noise for determined periods of use through the use of a storage capacitor, which is provided in addition to the charge reservoir and to which electric charges are supplied so as to be regulated in a determined manner and wherein electric charges are discharged from this storage capacitor. In addition, the high voltage can be quickly increased and reduced, which is particularly important, for example, in the above-mentioned optoelectronic distance measuring devices that are outfitted with APDs, when the avalanche amplification of the APDs should or must be adapted quickly to different environmental conditions.
The method, according to the invention, for generating high voltage from a low-voltage supply source, comprises a first step, in which a charge reservoir is charged via a charge pump to a voltage above a desired high voltage, and a second step, in which a regulated charge is effected from the charge reservoir to a storage capacitor, which is to be charged to the high voltage to be generated. In a third step, when the storage capacitor is overcharged, a regulated discharge takes place.
The first and second switching arrangements are preferably, controllable current sources, which are controlled by a regulator, wherein a signal corresponding to the actual high voltage at the storage capacitor is applied to the actual-value input of the regulator, while a signal corresponding to the desired high voltage at the storage capacitor is applied to the respective reference-value input.
Alternatively, the first and second switching arrangement can be a controllable switch with a charging and discharging resistor connected in series with the respective switching path; these switches are controlled by a regulator, wherein a signal corresponding to the actual instantaneous high voltage at the storage capacitor is applied to the actual-value input of the regulator, while a signal corresponding to the desired high voltage at the storage capacitor is applied to the reference-value input.